Zigzag Level Order Traversal in DSA C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Zigzag Level Order Traversal in a binary tree?

It is a way to traverse a binary tree level by level, but alternating the direction of traversal at each level. For example, left to right on one level, then right to left on the next.

beginner

Which data structure is commonly used to implement Zigzag Level Order Traversal?

A queue is used to process nodes level by level, and sometimes a stack or reversing the order is used to alternate the direction.

intermediate

How do you decide the direction of traversal at each level in Zigzag Level Order Traversal?

You use a boolean flag or a counter to track the current level. If the level is even, traverse left to right; if odd, traverse right to left.

beginner

What is the time complexity of Zigzag Level Order Traversal?

The time complexity is O(n), where n is the number of nodes in the tree, because each node is visited exactly once.

intermediate

Why might you use Zigzag Level Order Traversal instead of normal level order traversal?

It can be useful to visualize or process tree data in a way that captures alternating directions, which might represent certain patterns or requirements in problems.

In Zigzag Level Order Traversal, what data structure is primarily used to hold nodes of the current level?

A Stack

B Linked List

C Queue

D Hash Map

A queue is used to process nodes level by level in order.

How do you alternate the direction of traversal in Zigzag Level Order Traversal?

A Always traverse left to right

B Reverse the order of nodes at every alternate level

C Use a stack only

D Traverse randomly

You reverse the order of nodes at every alternate level to achieve zigzag pattern.

What is the output of Zigzag Level Order Traversal for a tree with only one node?

A [[root, root]]

B []

C [root]

D [[root]]

The traversal returns a list of levels, so a single node is [[root]].

What is the time complexity of Zigzag Level Order Traversal?

A O(n)

B O(n^2)

C O(log n)

D O(1)

Each node is visited once, so time complexity is O(n).

Which of these is NOT a typical step in Zigzag Level Order Traversal?

A Sorting nodes by value at each level

B Reversing node order on alternate levels

C Using a flag to track direction

D Using a queue to track nodes

Sorting nodes by value is not part of zigzag traversal.

Explain how you would implement Zigzag Level Order Traversal on a binary tree.

Think about how to process nodes level by level and flip direction each time.

Describe the difference between normal level order traversal and zigzag level order traversal.

Focus on the direction of traversal at each level.